| Melow Ltd | Wholesale & retail | 2022 |
| Melrix Ltd | Wholesale & retail | 2025 |
| Melrose Avenue Estates Management Ltd | Real estate | 2021 |
| Melusine's House Ltd | Hospitality | 2016 |
| Melva Apartments Ltd | Hospitality | 2010 |
| Melvin Properties London Ltd | Real estate | 2013 |
| Melvyn Allen Holdings Ltd | Financial services | 2025 |
| Melwood Wealth Management Limited | Professional & scientific | 2021 |
| MEM Sports Consultancy Limited | Professional & scientific | 2023 |
| Membarz Only Ltd | Wholesale & retail | 2024 |
| MEMORISS71 Limited | Wholesale & retail | 2025 |
| Memory Jump Ltd | Manufacturing | 2025 |
| Memory Lane Cakes Limited | Manufacturing | 1997 |
| Memory Lane Games (UK) Limited | Information & communication | 2021 |
| Memory Tree Retail Solutions Limited | Information & communication | 2019 |
| Memorymakers Limited | Wholesale & retail | 2025 |
| Men's Fashion Class Ltd | Wholesale & retail | 2018 |
| Mena Launcher Ltd | Administrative & support | 2025 |
| Menai Meats (Wales) Limited | Wholesale & retail | 2012 |
| Menai OJ Consultancy Limited | Professional & scientific | 2022 |
| Menasino Foundation Ltd | Professional & scientific | 2025 |
| Mence and Clark Tree Services Limited | Administrative & support | 2017 |
| Mend & Match Ltd | Information & communication | 2025 |
| Mend-A-Dent Limited | Manufacturing | 2005 |
| Menes Toni Driving Services Ltd | Construction | 2013 |
| Menest Ltd | Real estate | 2020 |
| Mengola Recruits Ltd | Administrative & support | 2020 |
| Mengtie Foreign Trade Ltd | Wholesale & retail | 2024 |
| Menha Ltd. | Information & communication | 2025 |
| Menlo Electric Limited | Administrative & support | 2023 |
| Menna Ltd | Information & communication | 2023 |
| Menons @ Property Limited | Real estate | 2020 |
| Menopause Academy Limited | Health & social care | 2019 |
| Menopause Chef Limited | Health & social care | 2019 |
| Menopause Retreats Limited | Health & social care | 2018 |
| Menstrwear Ltd | Wholesale & retail | 2025 |
| Mentality Clothing Co. CYF | Wholesale & retail | 2023 |
| Mentek Limited | Information & communication | 2021 |
| Menter Business Advisors Limited | Professional & scientific | 2003 |
| Menter Iaith BRO Morgannwg | Arts & recreation | 2014 |
| Mentis Recruitment Ltd | Information & communication | 2023 |
| Mentium Limited | Financial services | 2017 |
| Mentor Digitals Ltd | Education | 2026 |
| Mentorix Ltd | Education | 2025 |
| Mentrau Amgueddfeydd AC Orielau Cenedlaethol Cymru / National Museums & Galleries of Wales Enterprises Limited | Wholesale & retail | 1989 |
| Menurio Ltd | Information & communication | 2021 |
| Menza Events Limited | Hospitality | 2026 |
| Meomics Precision Medicine Ltd | Professional & scientific | 2021 |
| MEP Building Services Ltd | Construction | 2019 |
| MEP Commercial Support Ltd | Professional & scientific | 2025 |
| MEP Surveying Limited | Professional & scientific | 2016 |
| MEP427 Limited | Real estate | 2025 |
| Mepco Mouldings Ltd | Manufacturing | 2011 |
| MER SER Ltd | Financial services | 2014 |
| Mera Piya Ltd | Wholesale & retail | 2025 |
| Meraki. Hardware Ltd | Wholesale & retail | 2021 |
| Meramere LLP | | 2022 |
| Merarts Ltd | Wholesale & retail | 2025 |
| Mercalix Capital Ltd | Wholesale & retail | 2019 |
| Merchandising World Limited | Manufacturing | 2017 |
| Merchbysimo Ltd | Wholesale & retail | 2023 |
| Merched Holdings Limited | Extraterritorial | 2015 |
| Merchsquad Ltd | Wholesale & retail | 2024 |
| Mercia UK Distribution Limited | Wholesale & retail | 2024 |
| Mercuratrix Ltd | Wholesale & retail | 2021 |
| Mercurius Global Exchange Ltd | Real estate | 2017 |
| Mercury 7 Training Ltd | Education | 2015 |
| Mercury Accounting and Tax Services Limited | Professional & scientific | 2011 |
| Mercury Events Management Ltd | Arts & recreation | 2020 |
| Mercury Labs Ltd | Information & communication | 2020 |
| Mercury Promotions & Events Ltd | Arts & recreation | 2019 |
| Mercyfilled Limited | Professional & scientific | 2022 |
| Mere Ecom Ltd | Wholesale & retail | 2025 |
| Mereburn Limited | Health & social care | 2025 |
| Mergeform Limited | Wholesale & retail | 1990 |
| Mergermotion Limited | Information & communication | 2025 |
| Merhaba Cafe and Restaurant Ltd | Hospitality | 2026 |
| Meria Ltd | Wholesale & retail | 2025 |
| Meric Group Ltd | Wholesale & retail | 2025 |
| Meridian Apparel Ltd | Wholesale & retail | 2019 |
| Meridian Consultancy Services Limited | Professional & scientific | 2004 |
| Meridian Intelligence Limited | Information & communication | 2025 |
| Meridian Membranes Ltd | Construction | 2018 |
| Meridian Restaurants Limited | Hospitality | 2014 |
| Meridians Trading Limited | Wholesale & retail | 2016 |
| Merikep Ltd | Financial services | 2021 |
| Merit Commercial Ltd | Wholesale & retail | 2026 |
| Meritton Capital Limited | Professional & scientific | 2025 |
| Meritus Talent Limited | Administrative & support | 2024 |
| Meritva Studio Limited | Wholesale & retail | 2025 |
| Merka Trade PC | | 2018 |
| Merkland Burn Hydropower Limited | Energy | 2024 |
| Merlent Investments Limited | Information & communication | 2017 |
| Merlin Brands Limited | Manufacturing | 2023 |
| Merlin Capital Co., Limited | Professional & scientific | 2012 |
| Merlin Foods Limited | Manufacturing | 2026 |
| Merlin Technologies Group Ltd | Professional & scientific | 2021 |
| Merlyn Financial Services Limited | Financial services | 2015 |
| Mermade Eunion Limited | Other services | 2017 |
| Mermaid Pictures Ltd | Information & communication | 2024 |